Effect of GPi pallidotomy on motor function in Parkinson's disease

The major motor disturbances in Parkinson's disease are thought to be caused by overactivity of the internal segment of the globus pallidus (GPi), in large part due to excessive drive from the subthalamic nucleus. The excessive inhibitory activity of GPi is thought to "brake' the motor thalamus and the cortical motor system to produce the slowness, rigidity, and poverty of movement characteristic of parkinsonian states. To test the hypothesis that direct reduction of Gpi activity can improve motor function, we studied the effect of GPi pallidotomy in 14 patients. The location of the GPi nucleus was confirmed by microelectrode recording before lesion creation. Standardised videotape recordings before and after operation were randomised and scored by a "blinded' evaluator. 6 months after surgery, total motor score in the "off" state had improved by 30% and the total akinesia score by 33%. The gait score in the "off" state improved by 15% and a composite postural instability and gait score by 23%. After surgery there was almost total elimination of drug-induced involuntary movements (dyskinesias), with a 92% reduction on the side contralateral to the pallidotomy. No patient had visual or corticospinal complications. In these patients GPi pallidotomy enhanced motor performance, reduced akinesia, improved gait, and eliminated the neural elements responsible for levodopa-induced dyskinesias.